High Cycle Fatigue Behaviour of Cu/Sn Intermetallic Compounds Prepared by Transient Liquid Phase Bonding Process

Abstract

Transient liquid phase (TLP) bonds using Cu-Sn system have been suggested as high strength and temperature resistant joints for power electronics applications. While the physical and mechanical properties of these joints has been investigated to some extent, studies on fatigue properties and long term reliability of TLP joints are scarce. In this work TLP bonding was performed to produce thin Cu-Sn intermetallic joints by using Cu and 97Sn3Cu solder alloy as interlayer. Different processing conditions resulted in three types of thin joints consisting of three phases (Cu3Sn/Cu6Sn5/solder remnants), two phases (Cu3Sn/Cu6Sn5) and a single phase (Cu3Sn) with an overall thickness of ≤ 20 μm. The shear strength of the TLP joint containing one or two high melting point IMC layers showed a significant temperature resistance up to 200°C. Fatigue studies of TLP joints were conducted by using a 3-point-cyclic bending test system operating at 20 kHz. The highest fatigue resistance was obtained for the single-phase Cu3Sn joints with superior shear and flexural resistance. The two phase joints (Cu3Sn/Cu6Sn5) showed a slightly lower lifetime than the three phase system containing IMCs and residual solder. Fracture surfaces analysis in correlation with static and cyclic mechanical properties, provided insight into the failure mechanism of the Cu-Sn TLP joints.